Traditional vacuum cleaners usually belong to two different categories called canister cleaners and upright cleaners. The canister vacuum cleaner comprises a housing enclosing an electric fan unit that creates an airflow from a vacuum cleaner nozzle through a tube shaft and a hose and further through a separating system comprising a porous bag collecting the dust before the air reaches the fan and leaves the housing to the ambient air. The upright vacuum cleaner differs from the canister cleaner in that the tube shaft and the hose are eliminated and that the nozzle, that often is provided with a rotating brush, is pivotally connected to the vacuum cleaner housing. The housing encloses the fan unit and the air pervious dust bag and is provided with a handle to move the complete vacuum cleaner on the floor.
In order to further clean the air before the air leaves the vacuum cleaners mentioned above additional filters are arranged after the dust bag as seen in the air flow direction. These filters are usually placed such that they can easily be removed and be replaced by a new filter. As an alternative certain filters might be taken away in order to be cleaned by manual operations or by washing or rinsing the filter in water and/or cleaning agents.
There are also so called cyclone vacuum cleaners on the market, see for instance EP 00850060.1, that are provided with a different type of dust separation system. Instead of using an air pervious collecting bag the dust is separated by means of a vortex created in a circular cyclone chamber. The particles are by means of centrifugal action directed outwards from the centre of the vortex and are collected in a collecting container whereas the cleaned air is taken out from the center of the vortex. The clean air is then sucked to the vacuum source and flows out from the vacuum cleaner to the ambient air. Even if the main part of the dust particles that are present in the dust laden air are separated by the cyclone a minor part of the particles follow the clean airflow out of the cyclone. Consequently also for this type of vacuum cleaners there is a need for filters in the air passages after the cyclone chamber in order to get an efficient cleaning of the air flowing out from the vacuum cleaner.
It is a disadvantage that the operator of all of the vacuum cleaners mentioned above has to remove the filter and replace it or clean it since replacement means that the consumer always has to keep an eye on the consumption of the filter and to buy new filters when necessary whereas cleaning means that the vacuum cleaner can not be used during the washing period and moreover demands for certain cumbersome activities from the operators side.
It has also been proposed, see WO 85/02528, to provide a vacuum cleaner with two electrical motors (FIGS. 1-4) each having a filter that is placed in a common dust collecting chamber. In order to clean the filters the airflow through each filter is reversed by means of the other motor. The same publication also shows a vacuum cleaner arrangement (FIGS. 5-6) that is provided with one motor and one main filter and an auxiliary filter the filters also being placed in a common dust collecting chamber. In order to clean the main filter the airflow is reversed and directed through the auxiliary filter. A clear disadvantage with the first arrangement is the need for two motors whereas there is no indication how to clean the auxiliary filter in the second arrangement.